Never start by saying your question is an idiots question. Idiots, in their own weird conception of the world, ask the most logic questions you can encounter.
Next, I don't know why you make that assumption in the beginning of your post. Whether you have or have not installed the JRE and JDK is information that does not help in answering your questions.
Finally: I find it very strange that you are desperate and confused about those questions. Any article or book that is an introduction to Java covers the JVM mechanism that is so fundamental to Java. And aside a global understanding of what it does I never questioned the details of how a 'Hello World' main method outputs text to the console. Or how Swing objects show up as GUI-elements in my Windows or my neighbours Linux machine.
Maybe I'm just one of those guys who doesn't care how a car engine works as long as the car gets me from A to B.